A 4.7 magnitude quake registered near Taupo turned out to be a seismic wave from the Kermadec Islands. Image/Geonet
For a fleeting few minutes, it appeared the East Coast of New Zealand had been rocked by a cluster of earthquakes.
The GeoNet website recorded a 5.4 magnitude quake at 7.04pm, some 120km north of Te Araroa.
It was apparently followed two minutes later by a 4.7 magnitude quake striking 55km south-east of Taupo. It was reportedly 6km deep and was felt as far away as Auckland and Wellington.
Another 3.3 magnitude quake hit 5km deep near Te Kaha at 7.22pm.
But the so-called quakes were quickly deleted from the site and GeoNet tweeted that a 6.0 earthquake in the Kermadecs had caused "ghost quakes".
The real quake hit just after 7pm around 100km south of Raoul Island, one of four islands in the Kermadecs. A 6.6 magnitude quake also hit there last night.
But the dozens of people in New Zealand who reported feeling the shakes this evening weren't imagining things.
GeoNet seismologist Dr Bill Fry said the seismic waves from the Kermadecs would have been felt here.
"Kermadec is prone to earthquakes - it actually represents one of the biggest hazards to New Zealand," he said.
A heightened tsunami risk meant seismologists here and around the world are monitoring the area carefully, he said.
"When something like this happens, we take the time to dive in and understand the earthquake the happened to get a better estimate of the size," he said.
The Kermadecs region would feel aftershocks, he said. "The most likely situation is that they don't get bigger, and it gets farther and farther between aftershocks - that's what we hope."
In 2014, a similar phenomenon happened after the 6.9 quake on Raoul Island in the Kermadecs.
GeoNet explained at the time that "ghost quakes" appeared on the network typically after a large regional source earthquake.
Its "very sensitive seismic equipment" picks up waves that earthquakes create.
"Our equipment gets confused by these waves and interprets these as being a smaller, locally-sourced earthquakes close by.
"These quakes are an unfortunate side effect of getting information out to the public as quickly as possible, instead of waiting up to a quarter of an hour for a person to locate and ensure these are authentic earthquakes."
